The invention relates to an interactive display system, comprising
a transmitter, for transmitting a periodic signal which is suitable for propagation through the air to PA1 a plurality of substantially pointlike receivers at respective fixed positions with respect to each other, whereas a relative position of the transmitter with respect to the plurality of receivers is manipulatable, the receivers being suitable for receiving said periodic signal, a first and a second receiver from the plurality feeding PA1 first phase difference measuring means, for measuring a first phase difference between said receiving the periodic signal at the first and second receiver, the first phase difference measuring means feeding PA1 location control means, for on the basis of a received phase signal controlling a target location on the display screen. PA1 the location control means are arranged for controlling the second coordinate of the target location with respect to the second coordinate axis, under control of the second phase difference signal, independent of the first phase difference signal. PA1 it is smaller than a mouse PA1 it does not need a tail PA1 it can be carried on the head
Such a system is known from the U.S. Pat. No. 4,885,433.
The object of the known system is to determine the position of the transmitter in a plane or in three dimensional space. In case of the plane, the device performs as a computer mouse and the target location is, for example, represented by a cursor on the display screen.
When the transmitter is moved in a plane and receivers are at known positions, a measured first phase difference between the receiving at the first and second receivers indicates that the transmitter must be located on a first two dimensional surface of positions in space. A similarly measured second phase difference between the receiving at a third and fourth receiver (one of which may be the second receiver), indicates that the transmitter must be located on a second surface in space. Using also the restriction that the transmitter lies in the plane, the position of the transmitter is determined by solving for the intersection of the first and second surface and the plane.
Alternatively, the known system uses a fifth and sixth receiver for determining a third phase difference which provides a third surface, which can be used instead of the plane when the position is solved by calculating the intersection of three surfaces.
The known system has the disadvantage that the position must be solved from a set of non linear equations defining the surfaces. This requires a substantial amount of computing power.